A. Field of Invention
This invention relates to impact printing machines and in particular to a novel and improved impact printing apparatus of the class employing a continuously rotating impeller to impact accelerating forces to one or more print hammers via one or more selectively actuable interposers.
In impact printers a plurality of type die are mounted upon a moving type carrier (such as a drum or an endless belt) which periodically presents the type die to an imaginary print line adjacent a printing medium including a document. A plurality of print hammer mechanisms are aligned with the print line and are responsive to electrical signals to selectively impact the document with selected ones of the moving type die to effect printing of characters representing the selected type die on the document.
B. Prior Art
Prior art printing mechanisms have used a source of mechanical energy such as a continuously rotating impeller with one or more impeller teeth which are aligned with corresponding print hammers. Associated with each impeller tooth and a corresponding print hammer is an interposer element which is selectively moveable from a normal position into the path of motion of the impeller tooth such that the impeller tooth engges the interposer driving it and the corresponding print hammer toward the print line to impact the printing medium with a selective type die. Heretofore such printing mechanisms have been characterized by rather complex interposer and print hammer linkages having a rather large number of parts which are difficult to assemble and/or maintain, and therefore, rather costly. In addition, such prior art printing mechanisms have used interposers which are rigid and nonflexible in the plane of motion of the impeller tooth and print hammer. The rotating impeller tooth engages such a rigid interposer rather abrubtly and imparts rapid and uncontrolled acceleration forces thereto. This results in normal wear or rapid deterioration of the material forming the interposer, print hammer and impeller. Because of this, expensive materials have had to be employed for such parts.